A modern architecture for a network switch comprises a multiplicity of modules, typically each provided on a respective silicon chip, wherein each module has a receiving section for processing data packets received on a multiplicity of ports, a switching section, which transmits those packets on one or other of a multiplicity of links, usually called ‘mesh’ links, and a transmitting section, which is connected to receive packets from a multiplicity of mesh links and provides for transmission of packets on one or other of a multiplicity of output ports. In a typical example, the switching section can direct packets to any one of four mesh links and the transmitting section can receive packets from any one of four mesh links.
One way of connecting such modules to form in effect a single switch is to connect one mesh link per module to the transmitting section of the same module and to connect each of the other three mesh links to a transmitting section in each of the other three modules. Although such a configuration is useful, it is not the only configuration in which a plurality of modules could be disposed.
An important restriction on the versatility of switching modules of this general character arises by virtue of the limited bandwidth of a mesh link compared with the total bandwidth available through the external ports of a module and the association of particular ports with a respective mesh link.
In an ordinary switch, a received data packet is usually subjected to an address look-up, wherein selected address data, which may be a media access control destination address or a network destination address is used to access a corresponding entry in a look-up table in order to obtain forwarding data for use by a switching engine. The forwarding data customarily includes a port number identifying an egress port from which the packet must be forwarded. The numbering or ID of the egress port will determine the mesh link to which the packet is directed. The look-up table can be at least partly established (as is well known) by making entries identifying, in each case an (ingress) port number with the source address of a packet received at the respective port.